They found that participants who reported a more positive mood also had higher levels of antibodies in their blood.

The study's senior author said there are a variety of factors that can affect how well a vaccine works, but believes the study suggests that mood is one of those factors. The study was published in the journal, "Brain, Behavior and Immunity."

Health officials said this year's flu strain is predominantly the A Virus, usually responsible for large epidemics.

Another reason to get your flu shot and make sure you're in a good mood.